The four-star admiral, who also heads the National Security Agency, said cyberwarfare “is one area we have to acknowledge that we have peer competitors who have every bit as much capacity and capability as we do.”

Russia, China, Iran and North Korea pose the greatest nation-state threats in cyberspace, and the Islamic State is mainly using cyber programs to recruit terrorists and propagandize, but could turn to cyberattacks against infrastructures in the future.

“The Russians I would consider in cyber a pure competitor,” Adm. Rogers said. “China is not in the same place, but rapidly attempting to get there.”

North Korea conducted a sophisticated cyberattack on Sony Pictures Entertainment in 2014 but has not launched a similar attack since.

Adm. Rogers told lawmakers his greatest concern is the “physical shutdown” of networks used for communications and logistics. A second major worry is cyber penetrations into critical military networks to manipulate data to provide false or misleading information that would cause warfighters to make disastrous decisions.